1. Field of the Invention
The present invention relates to techniques for improving the throughput and reliability of wireless links by bonding communication channels together. More particularly, the invention relates to techniques for using multi-beam antennas to communicate with spatially separated wireless access points that are then bonded to increase channel bandwidth.
2. Description of Related Art
It is well known in the art to increase the bandwidth and reliability of a communication interface by combining, or bonding, two or more sets of interface hardware. A network interface card on a host computer, for example, may be limited to a certain maximum data rate. A second network interface card can be added to the host computer, and software running on the host computer can be made to divide up information packets across the two network interface cards such that portions of a message to be transmitted are sent over both network interface cards simultaneously. If each network card operates at its full bandwidth, the combined bandwidth of the entire system is effectively doubled. At the receiving end, the two network data streams are received simultaneously, and the receiving computer reassembles the transmitted data message by properly organizing the packets received from each of the two network interface cards.
Alternatively, the technique of adding a second network interface card to a host computer can be used to create redundancy for the transmission of important data. In this case, the host computer sends the same data packets over two independent network interface cards. The receiving computer compares the incoming data from the two channels to assure that the data is received without error. If a mismatch between the two channels is discovered, the receiving computer can request a retransmission of the corrupted data.
The channel bonding methods described above are generally applied to hard-wired connections over copper wire or fiber optics because such hard-wired systems provide good isolation between the two or more independent communication channels. When channel bonding is attempted over wireless networks, interference between the multiple wireless network cards can cause communication failures or excessively high error rates. To minimize interference, the multiple wireless systems can be tuned to different frequency channels. However, of the eleven channels in the 2.4-GHz frequency band of the IEEE 802.11b and g wireless standards, only channels 1 and 11 are spaced sufficiently far apart that they may be used simultaneously without excessive interference, limiting the channel-frequency choices. Furthermore, equipment that uses channel bonding on channels 1 and 11 will effectively use up the entire 802.11 spectrum, locking out any other wireless networks in the broadcast area. As a result of the competition for bandwidth of multiple network users, the overall data throughput may actually decrease.
A solution to this problem is to spatially separate the wireless data streams that are to be bonded in order to reduce interference from simultaneous transmissions that are at or near the same frequency. Current wireless network cards and laptop computer systems use omni-directional, low-gain antennas to communicate with wireless access points. Such antennas provide little spatial discrimination and are thus not suitable for this purpose. However, providing a dedicated processor to generate spatially separated beams can add significant complexity and cost. Accordingly, it would be useful to provide a wireless system that can communicate simultaneously over multiple, spatially separated beams that can be bonded into a single virtual channel to provide increased data bandwidth and/or improved communication channel reliability. It would further be useful to use existing processor resources to support digital beam forming to create a low-cost smart DBF antenna for consumer electronics.